The present invention relates generally to filtering apparatus, such as dust collectors or the like, and, in particular, to a filter unit utilized in apparatus of this type.
One well-known type of industrial filtering apparatus is a dust collector that utilizes, as the filtering medium, a large number of fabric bags that have a tubular configuration and a substantial lengthwise extent. The dust collector includes a partition plate that separates the clean air compartment from the dirty air compartment of the dust collector, and this partition plate is formed with a large number of openings arranged in a pattern, and a fabric filter bag is mounted to the partition plate at each such opening, whereby the filter bags depend vertically from the partition plate into the dirty air compartment and the interior of the bags are in open communication with the openings in the partition plate. When a pressure drop is imposed across the partition plate and the filter bags by a blower or the like, the air with entrained dust or the like is caused to flow from the dirty air chamber through the fabric of the filter bag to the interior thereof, thereby depositing dust on the exterior surfaces of the filter bags and causing the cleaned air to flow from the interior of the bags and through the openings in the partition plate into the clean air compartment. In virtually all dust collectors of this type which are in use today, some apparatus is provided for cleaning the bags at periodic intervals, such as by utilizing a reverse flow of air or a pulse jet of air to separate collected dust from the exterior surfaces of the bags so that it can be collected in a hopper and removed from the apparatus. Typical examples of dust collectors of the foregoing type are disclosed in U.S. Pat. Nos. 3,648,442, 3,951,627 and 4,157,899.
Because the fabric material from which the filter bags are formed is generally flaccid, the air flow through the bags and the pressure drop thereacross will tend to collapse the bags and thereby reduce the exposed surface area of the bags that is available for filtering the air. Accordingly, it is common practice to provide each filter bag with a cylindrical wire cage that is rigid and that extends lengthwise within the interior of the bag to provide a rigid support that prevents the bag from collapsing inwardly, and the bag is therefore maintained in its generally tubular or cylindrical configuration.
While these wire cages significantly increase the efficiency of the dust collectors by maintaining the bags at their fully expanded dispositions, they present problems in terms of removing a bag from its mounting in the partition plate when it becomes necessary to replace an exhausted bag with a new bag, and similar problems are encountered when the new bag is installed in the opening of the partition plate.
Space requirements and/or application variables sometimes allow a dust collector to be designed so that personnel who replace the old filter bag unit with new ones must enter the dust collector only in the clean air compartment above the partition plates in which case the old filter bag units are removed upwardly through the openings in the partition plate and the new filter units are inserted downwardly through such openings. In one known arrangement, the filter bag is dropped through an opening, but one end portion of the bag is maintained at the top surface of the partition plate until a rigid wire cage is inserted downwardly into the bag, the rigid wire cage being formed with an enlarged end portion having a diameter greater than the diameter of the opening in the partition plate so that this enlarged portion can engage the end portion of the bag and hold it in place against the upper surfaces of the partition plate. In many instances, a clamp or other retaining member is then screwed into the partition plate and arranged to engage the enlarged portion of the rigid wire cage and hold it in place. In an improved version of this arrangement, the end portion of the fabric bag is provided with an embedded snap band spring that urges the bag into engagement with the opening in the partition plate. The rigid wire cage has an enlarged portion having a cup-like inverted U-shape to engage the end portion of the bag above the partition plate, and it is also provided with a resilient indent located just beneath the partition plate that bulges outwardly to cooperate with the rigid enlarged cap portion of the wire cage in holding the bag in place without requiring the screw and retaining member of the earlier version described above.
In other applications of industrial dust collectors, because of overhead space restrictions (i.e., existing buildings with low ceiling heights), the exhausted bags must be removed by workmen located in the air chamber beneath the partition, and in such dust collectors it will be apparent that the filter units described above cannot be used because the rigid enlarged portion of the wire cage is too large to permit it to be inserted upwardly through the openings in the partition plate. Thus, in these types of dust collectors, a special filter unit is provided which includes a conventional filter bag and a wire cage that is slightly shorter in length than the bag, and the wire cage is provided at its upper end with an annular metal band formed with a slit so that the diameter of the band can be changed. The metal band is also provided with an annular groove extending around its circumference. To install a new filter unit it is necessary, first, to insert the cage into the filter bag, and then fold the excess length of the filter bag into the cage about the upper edge of the annular metal band. The filter unit is then pushed upwardly onto and about a short depending circular wall located beneath each opening in the partition plate. This circular wall is provided with a projection, or reverse groove, that interfaces with the groove in the metal band of the cage to locate the filter unit in place on the circular wall, and a conventional hose clamp is then fitted around the filter bag and the metal band of the wire cage and tightened up using an appropriate tool. Thus, the end of the filter bag is held between the circular wall of the partition plate, which in some instances consists of the lower end of a venturi located in the openings of the partition plate for use with pulse jet cleaning apparatus, and the metal band of the wire cage. However, it will be apparent that the removal of an exhausted bag and the installation of a new replacement bag will require considerable time and effort because of the various steps that are required, some of which necessitate the use of special tools.
The present invention provides a unique filter unit which has universal application in that it can be used, without structural modification, for either a top-loading or a bottomloading dust collector, and, additionally, it provides a number of advantages compared to the conventional filter units described above.